The present invention relates to an amphibious vehicle.
Amphibious vehicles capable of powered travel on both land and water are known. In order to improve the performance of amphibious vehicles on water, various systems have been developed to allow the wheels to be retracted above the water line when the vehicle is water-borne. Such a system is known, for example, from the applicants' International patent application WO95/23074, which describes an apparatus that enables an axle-driven wheel to move between a protracted position, in which it has a substantially horizontal axis of rotation for support of the vehicle on land, and a retracted position, in which the axis of rotation of the wheel is at an angle greater than 45 degrees to the horizontal.
In a typical known retractable wheel arrangement, the wheel is mounted to the body of the vehicle by means of one or more suspension linkages which are configured to allow the wheel to move between the protracted and retracted positions. Normally an actuator, such a hydraulic strut or ram, will be operatively connected to one of the suspension linkages to move the wheel between the protracted and retracted positions. Also connected to one of the suspension linkages is a suspension means comprising springing and damping means for absorbing road shocks when the vehicle is used on land. Various types of suspension means have been proposed for use with the known retractable wheel apparatus, such as: coil spring and hydraulic damper struts, torsion bar and damper systems, and hydropneumatic suspension units.
A drawback with known retracting wheel arrangements is that the design of the suspension means may have to be compromised in order to allow the wheel to be retracted. For example, it may be necessary to design the suspension means so that it can be fully compressed when the wheel retracts or it may be necessary to alter the sizes and shapes of components to enable full retraction of the wheel to take place. As a result, it may be difficult and time consuming to tune the suspension characteristics of the vehicle for land use. For example, users of the vehicle will expect ride comfort characteristics on land which are comparable to those of a conventional land based motor vehicle.
A further drawback of some known wheel retraction arrangements is the amount of space required to accommodate movement of the suspension means as the wheel moves between its protracted and retracted positions. U.S. Pat. No. 4,958,584, for example, describes an amphibious vehicle having a wheel retraction arrangement in which the wheel is attached to the vehicle body using a wishbone type suspension. A suspension means in the form of a strut having a coil spring located about a telescopic hydraulic damper is connected between an upper wishbone and part of the wheel retraction system. To move the wheel to the retracted position, the upper end of the strut is drawn inwardly. This arrangement takes up a considerable amount of space in a central area of the vehicle making it unsuitable for use with a compact amphibious vehicle. The problem is most acute where the engine and transmission are mounted between a pair of retractable road wheels, as there is little space available into which the struts for those wheels can be drawn.